High-Output-Current Boron-Doped Single-Crystal Diamond MOSFETs with a Thin Boron-Doped Epitaxial Layer

High-output-current boron-doped diamond (B-diamond) metal-oxide-semiconductor field-effect transistors (MOSFETs) with a modulated boron-doped epitaxial layer were fabricated. An intrinsic diamond epitaxial layer was deposited on the single-crystal diamond substrate as a buffer layer, and plasma-enhanced chemical vapor deposition (PECVD) SiO₂ was employed as both the gate dielectric and passivation layer. The boron-doped epitaxial layer has a thickness of approximately 500 nm and a boron concentration in the range of 10¹⁷-10¹⁸ cm^-3. The B-diamond MOSFETs showed clear p-channel operation, with a maximum output current of -0.18 mA/mm at room temperature. When the temperature was increased to 150 °C, the maximum output current increased to -1.05 mA/mm, while the on-resistance decreased from 413.91 to 12.13 kΩ·mm. The on/off ratio remains approximately 10⁵ over the measured temperature range. In addition, the device exhibited a breakdown voltage of -347 V at a gate-to-drain spacing of 12.5 μm, and the simulation results showed that the peak electric field was mainly concentrated near the drain-side gate edge of the passivation layer. These results indicated that, for the B-diamond MOSFETs, a balanced epitaxial layer thickness and boron concentration were essential for achieving sufficient channel conduction as well as effective gate control ability.